Stabilization of styrene-acrylonitrile polymers with alkyl-substituted phenols and vic-epoxy compounds



United States Patent STABILIZATION OF STYRENE-ACRYLONITRILE POLYMERSWITH ALKYL-SUBSTITUTED PHE- NOLS AND VIC-EPOXY COMPOUNDS Arnold B.Finestone, Leominster, and James S. Pavlin, Fitchburg, Mass., assignorsto Foster Grant Co., Inc., Leominster, Mass, at c tion of Delaware NoDrawing. Filed Oct. 7, 1960, Ser. No. 61,094

9 Clairns. (Cl. 260-23) This invention relates generally to new andimproved stabilized polymeric compositions consisting essentially ofcopolymers of vinyl aryl compounds and acrylonitrile. More particularly,this invention relates to new and improved thermoplastic polymericcompositions consisting of from about 65% to about 80% by weight ofvinyl aryl compounds and from about 35% to by weight of acrylonitrilehaving incorporated therein a combination of two additives, i.e. anepoxidized organic composition, and a substituted phenol.-

The polymeric compositions of this invention are known assolvent-resistant resins, viz. resins that are relatively resistant toattack by such liquids as gasoline, alcohol, water, aqueous acids andaqueous bases, even though they are swellable and/or dispersible in suchliquids as methyl ethyl ketone. As molding compositions, they arereadily moldable to clear and substantially non-discolored products byconventional means such as by compression or injection molding, hotpressing, extrusion or the like.

Thermoplastic resinous compositions of from about 65% to 80% by weightof vinyl aryl'compounds and from about 35% to 20% by weight ofacrylonitrile are known. These copolymers, which form the basis of thepresent invention. have average molecular weights such that 10% byweight solutions of the copolymers in methyl ethyl ketone haveviscosities between 6 and 40, preferably between 10 and 30, centipoisesat a temperature of C. The copolymers usually possess the most desirablecombination of mechanical properties, viz. strength, hardness,flexibility, and molding behavior, viz., flow rate, which combination ofmechanical properties and molding behavior is related to the averagemolecular weight of the copolymers. 7

Several methods of preparing such thermoplastic resinous compositionsare known to the art. For example, bulk, solution, suspension andemulsion polymerization techniques have been employed.

Both thermal bulk polymerization and thermal solution polymerization ofstyrene and acrylonitrile may be carried out at temperatures rangingfrom about 60 C. to about 180 C. under pressure. When thermal solutionpolymerization techniques are employed, hydrocarbon diluents such asbenzene, ethylbenzene or the like are used, and such a polymerizationprocess usually requires elaborate equipment to control the reaction andto remove unreacted monomers and/or diluents. In such a polymerizationit has been found advantageous to avoid the use of organic catalystsbecause of their ellect on the acceleration of the reaction rate thusincreasing the potential for an uncontrollably strong exothermic orrunaway polymer reaction.

Also known in the art is the polymerization of styrene and acrylonitrilein the presence of an emulsifying agent.

ice

Products thereby produced have not received commercial acceptancebecause of the great difiiculty in obtaining a clear and non-discoloredproduct. In emulsion polymerization systems, it is necessary to takeprecautions to control the ultimate molecular weight of the finalproduct, and because of the high water solubility of acrylonitrile, itis extremely difficult to obtain a uniform product. In general, a higherpercentage of acrylonitrile than that required in the copolymerizationis usually charged to a reactor in order to compensate for thesolubility of the monomer in water. Ordinarily, emulsion systems arecatalyzed by water soluble peroxy compounds, in amounts from 0.001 to1.0% of the polymerizable monomer. Examples are, hydrogen peroxide,sodium peroxide, the sodium salts of other peroxy acids, the potassium,ammonium and other water soluble salts of the above or other peroxyacids and any other water soluble compounds containing a peroxy group(-OO) which can generate radicals. The uniform distribution of thereagents in the reaction mass can be accomplished by agitation or by theuse of wetting agents or emulsion stabilizers.

Commonly used wetting agents or emulsion stabilizers include the watersoluble or dispersible salts of fatty acids, such as sodium oleate andpotassium stearate, mixtures of water soluble fatty acid salts, such asthe common soaps prepared by the saponification of animal and vegetableoils, the amino soaps such as triethanol amine I and dodecylmethylamine, sulfonated hydrocarbons such as alkyl aryl sulfonate andothers. The quantity of emulsifying agent usuallywill depend upon theparticular agent selected, the ratio of water and monomerto be used, andother conditions of polymerization. In general, however, from 0.5 to 5%by weight of the monomer, may be employed.

It is also known in the art that the polymerization of styrene andacrylonitrile can be carried out in aqueous suspension, i.e., in thepresence of a suspending agent, and that the products thereby made alsohave not received commercial acceptance because of the great difiicultyin producing non-discolored uniform products. With respect to suspensionpolymerization, a relatively clear product can be obtained because ofthe ease with which the suspending agent is removed, but the product isunfavorably limited bythe color produced. Again, as with the emulsionsystem, a greater concentration of acrylonitrile must be charged to areactor in order to compensate for the solubility of the acrylonitrilein water.

Normally, suspension polymerization is accomplished" at temperaturesvarying between C. and 130 C. and preferably between C. and C. in thepresence of a catalyst and a dispersing or suspending agent. It is wellknown that peroxides such as benzoyl peroxide,

acetyl peroxide, tertiary butyl hydroperoxide and diazo compounds suchas azo'bis-isobutyrylnitrile can be used as catalysts in thepolymerization of styrene type com pounds with acrylonitrile. Commonlyused suspending agents include calcium hydroxy-apatite, tricalciumphosphate, talc, polyacrylamide, methyl cellulose, methyl starch, glycolcellulose, polyvinyl alcohol, styrene-maleic acid copolymers, etc.

It is dilficult to prepare consistently good polymeric products in theforegoing proportions which are readily moldable to clear andnon-discolored products and which have satisfactory mechanical andmolding behavior. The reasons, therefore, are quite evident. That thecopolym- 35% of the total amount of the monomers.

. tion temperature. At temperaturesat which the copolym- -erization isreadily controlled, the rate of production of the copolymer isundesirably slow and the molecular weight of the copolymer isundesirably high. On the other hand, polymerization at temperaturescalculated .to give desirable average molecular weight results in areaction rate so great as to make its control diflicult.

vIn general therefore, raising the temperature at which suspensionpolymerization is carried out for the purpose of lowering the molecularweight of the product is usually undesirable sinceit involves aconsiderable increase in therate of reaction and may result in either orboth an uncontrollably strongly exothermic or runaway" polymer reactionand discoloration of the polymeric product by overheating.

wherein n is an integer greater than two, preferably an integer from 6to 16, such a catalyst being exemplified by caprylyl, octanoyl, lauroyl,myristyl and stearyl peroxide and a third comonomer of the monovinylaromatic type, i.e., alpha-methylstyrene. The styrene acrylonitrilepolymers thus prepared in the presence of the aforementioned insolublealiphatic peroxide catalyst and the monovinyl compound such asalpha-methylstyrene have relatively high uniformity, relatively goodcolor, and relatively good color stability and do not appreciablydiscolor and are readily moldable to substantially clear andnon-discolored shaped products by conventional means,

- as more .fully disclosed and claimed in our co-pending U.S.application Serial No. 21,146, filed April 11, 1960.

More specifically, as disclosed in our co-pending application, desirablepolymeric compositions consisting essentially of from about 65% to 80%by weight of styrene and'alpha-methylstyrene and from about 35% to about20% by weight of acrylonitrile can be produced by suspensionpolymerization in the presence of a catalyst of the aforementioned type,the comonorner alpha-methylstyrene beingpresent in the proportion offrom about to The percentage of alpha-'methylstyrene may be somewhatreduced in some cases, by incorporation in the system of a chaintransfer agent, i.e., mercaptan, aliphatic halogenated compounds,aromatic hydrocarbons, unsaturated dimers of monomeric alpha-alkylaromatic compounds, i.e., the dimer of alpha-methylstyrene, etc.

Preparation of the polymer by suspension polymerization in accordancewith our aforementioned applica tion is carried out by copolymerizing amonomer charge consisting of 20 to 35 parts of acrylonitrile, 2 to 10parts acrylonitrile in excess, and from 80 to 65 parts of styrene andalpha-methylstyrene in an aqueous suspension at temperatures betweenpreferably about 65 C. and about 90 C. in the presence of a waterinsoluble aliphatic peroxide catalyst as described above. The catalystis present in the aqueous suspension in amounts of from about 0.02% to2.0%, and preferably between .1 to 1.6% by weight of the-combined weightof the monomers charged. Most efiicient polymerization is achieved bycontrolling polymerization so that it may be stopped at a conversion inthe range of from 60 to 92% preferably between 65 to 85%.

When thermal bulk polymerization techiques are employed, conversion isstopped within a range of about to 90% while in conventional emulsionpolymerization systems about to 92% conversion is affected. In allmethods of polymerization, if polymerization is carried beyond thedesirable limit, a non-uniform copolymer will be produced probably sincelong'units of acrylonitrile in the chain are sites of .thermaldiscoloration either by an intermolecular reaction or by anintramolecular cyclization.- conversions acrylonitrile in the copolymerhas a tendency to crosslink and gel withattendant disadvantages to theproduct. p

While the method of preparing polymeric compositions consistingessentially'of vinyl aryl or styrene compounds and acrylonitrile by theabove specific suspension polymerization procedure has succeeded 'inproducing copolymer products which are clear and readily mold able tosubstantially clear and non-discolored products, we have found thatthese products can-be substantially improved in these respects by theincorporation therein of two classes of organic additives.

More specifically we have now found that the incorporation of each oftwo additives, i.e., an epoxidized composition and a substituted phenol,in polymeric compositions consisting ofv from about to about 80% byWeight of vinyl aryl compounds andfrom about 35% to 20% byweight ofacrylonitrile, and having the previously recited average molecularweights, improves .the stability of the polymeric compositionsmostunexpectedly regardless of process, i.e., bulk, solution, emulsionor suspension, employed. Molding of these polymeric compositions atrelatively high temperatures does not result in loss of clarity butunexpectedly in production of substantially non-discolored products. I

The phenol type compounds which can be used to advantage in the processof our invention include substituted phenols wherein the 2 and 6positions on the benzene ring are substituted with organic radicals with2, 4, 6, tri substituted phenols being preferred. Phenols givingbestresults are those wherein the 2 and 6 positions are substituted withbranched chain groups, i.e., substituents wherein the carbon chainscontain secondary or tertiary carbon atoms. These compounds prescribe,to the general formula:

1'1. wherein R R and R are ahphatic, aromatic substituted aliphatichydrocarbons or mixtures thereof each containing no more than 12 carbonatoms. Illustrative examples include 2,6 di-t-butyl'p-cesol,, 2,6di-Z-isooctyl pcresol, 2,4,6 tristyryl phenol, 2,4,6 tri-2-octyl phenol,2,6

-distyryl-p-cresol, 2,6 diisopentyl p-cresol, 2,6 di-alpha:

methylstyryl p-cresol, etc. It will be obvious that mixtures of theabove substituted phenol compounds can be employed.

Processes and compositions utilizing stabilization with the above phenoltype compounds are the subject of co pending application Serial No.421,684, filed December 28, 1964, which is a continuation of applicationSerial No. 61,093,.filed October 7, 1960, now abandoned.

Moreover, it is generally known that at'high from about 4 down to 1depending upon the of the polyhydroxy compound employed.

Polyhydric phenols which have been found particularly suitable inpreparing epoxy resins useful in this invention are the reactionproducts of phenol and aliphatic ketones, including polynuclear phenolswherein the phenol nuclei are joined by carbon bridges such as p,pdihydroxydiphenyl dimethyl methane, p,p dihydroxydiphenyl methane, tris(p-hydroxyphenyDmethane, and 2,2,5,5 tetra. (parahydroxyphenyl)hexane,etc. Examples of additional polynuclear phenols are those in which thephenol nuclei are joined by other than carbon bridges such as his(p-hydroxyphenyl)sulfone, etc.

Suitable polyhydric alcohols used in preparing the present epoxy resinsinclude glycerol, propylene glycol, 1,4 butanediol, pentaerythritol,etc.

The second type of epoxidized compositions suitable for use in ourinvention are those epoxy oils resulting from the epoxidation of suchwell known natural products as unsaturated oils which are glyceridesresulting from the esterification of trihydric alcohol glycerol withhigher and middle fatty acids, i.e., plant oils, olive oil, rape oil,almond oil, peanut oil. palm oil, and soybean oil, etc. Oils of theterpene series such as bornylene, camphene, carene, dipentcne, fenchene,limonene, pinene, terpinene, etc., may also be epoxidized and aresuitable for use in this invention. Well known epoxidizing agents suchas peracetic acid may be employed to form these epoxidized compositions.The natural products are preferably substantially epoxidized so as toyield the highest oxirane concentration possible in each molecule.

The third type of epoxidized compositions which we have found to besuitable for use in the present invention are the low molecular weightmaterials obtained from the cpoxidation of cycloaliphatic compounds.Examples of useful products include dicyclopentadiene dioxide,di(isodecyl 4,5 -epoxycyclohexane- 1 .Z-dicarboxylate, 3,4-epoxy- 6,methyl cyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, di(2ethylhexyl)4,5 epoxycyclohexane- 1,2-dicarboxylate. etc. The oxiraneoxygen content of these materials preferably is high and is obtained bysubstantially complete epoxidation of the double bonded carbons in themolecules. It is desirable, when using the second and third types ofepoxidized compositions that the oxirane content be as high as possibleand since low molecular weight liquid epoxy compounds are high inoxirane oxygen content they are preferred.

The additives employed in this invention are most advantageouslyincorporated in the vinyl aryl and acrylonitrile material prior to thepolymerization thereof, the epoxidized compositions may also be addedduring or after the polymerization.

In general, the phenol type compounds may be employed in amounts rangingfrom about 0.005 to 0.9% by weight of the initial monomers employed withfrom about 0.01 to 0.5% by weight being preferred. The epoxidizedcomposition is usually used in amounts ranging from about 0.005 to 0.75%by weight of the initial monomers employed with from about 0.01 to 0.5%by weight being preferred. The concentration of the epoxy compositionvaries within the broad range specified depending on the particularoxirane content of the molecule in the specific epoxy employed.

The vinyl aryl, i.e., styrene type compounds which can be used inpreparing the copolymers of our invention are those compoundsrepresented by the following formula:

functionality (Rilu wherein R is selected from the group consisting ofhydrogen and the methyl radical, R is a substituent selected from thegroup consisting of chlorine and lower alkyl radicals and n is aninteger between 0 and 2. Included are styrene per se, nuclearsubstituted alkyl styrenes, e.g., o-,

mand p-methyl styrene, 2-4 dimethyl-styrene and the like, alpha and betaalkyl substituted styrenes, e.g., alphamethylstyrene and the like.Mixtures of styrene compounds may also be employed, i.e., a mixture ofstyrene and alpha-methylstyrene as set forth above.

In place of acrylonitrile, methyl substituted acroylonitrile may beemployed to advantage in preparing the compositions of this invention.

A scale of color index numbers for visually comparing the polymericmaterials of this invention with each other and with polymers made bythe same methods but not incorporating-the additives herein disclosedhas been devised. Molded examples for comparative purposes were preparedby pressing polymer beads into plaques at 370 F. and 450 F.,respectively, for 10 minutes. The scale in which the number is relatedto its adjacent color is as follows:

The following examples illustrate the invention, but are not to beconstrued as limiting. In these examples parts are by weight, unlessotherwise specified.

coat-bro Example 1 To a suitable pressure reaction vessel containing 200parts of distilled water are added 50 parts of styrene monomer, 15 partsof alpha-methylstyrene monomer, 35 parts of acrylonitrile, 1.4 parts oflauroyl peroxide. The monomer mixture is polymerized at a temperature of80 C. in an inert atmosphere under autogenous pressure. Calciumhydroxyapatite precipitated by a reaction between the required amountsof trisodium phosphate and calcium chloride is used as suspending agent.The degree of conversion is controlled by removal of the unreactedmonomer through steam distillation. Upon completion of thepolymerization, the polymer beads are thoroughly washed with water anddried in an air drier at C. to C. In the final copolymer there is a25.5% of combined acrylonitrile, by weight of the copolymer. The polymerso formed has a viscosity of 16.2 centipoises when measured as a 10% byWeight solution in methyl ethyl ketone at 25 C. A portion of the polymerbeads is pressed into a plaqueat 370 F. and held at that temperature for10 minutes. other portion of the heads is pressed into a plaque at 450F. and held at that temperature for 10 minutes. The color index numberof the molded plaque is 14.

Example 2 Example 1 is repeated substituting benzoyl peroxide for i thelauroyl peroxide.

Employing the test molding conditions of Example 1 on i the resultantproduct, the color index number of the test plaque molded at 370 F. and450 F. is greater than 20.

Example 4 Example 1 is repeated with the addition before polymer-izationof 0.01 part of 2,6 di-Z-isoocty-l p-cresol and 0.01

The color index number is 7. An-

i 450 F. is 6.

35 parts of acrylonitrile.

7 part of Epon828, a polymer of epichlorohydrin and bisphenol A havingan average molecular weight of 390 grams and an epoxy equivalencyof0.54/ 100 grams. Employing the molding conditions of Example 1, thecolor index number of the test plaque molded at 370 F. is and the colorindex number of the test plaque molded at Example 5 Example 2.isrepeated with the addition before polymerization of 0.1 part of the Epon828 of Example 4 and 0.33 part of 2,6 di-t-butyl p-cresol. Employing themolding conditions of Example 2, the color index number of the testplaque molded at 370 F- is 7 and the test plaque molded at 450 F. hasacolor index of 12.

- Example 6 To a suitable reaction vessel containing 200 parts of ditilled water are added 65 parts of styrene monomer, and An alkyl benzenesulfonate having anaverage of 24 carbon atoms per molecule is employedas the emulsifying agent and 0.2 gram of potassium persulfate isemployed as catalyst. The mixture is polymerized in emulsion withconstant agitation at 45 C. until approximately 85% conversion isobtained. The polymeric material is coagulated, washed with warm waterand evaluated for color as in Example 1. The color index number of theplaque molded at 370 F. is and the color index number of the plaquemolded at 450 F. is greater than 20. g

- Example 7 Example 6 is repeated with the addition beforepolymerization of 0.5 part of 2,4,6 tristyryl phenol and 0.3 part of theepoxidized soybean oil of Example 3; Employing the molding conditions ofExample 1 on the resultant product, the color index number of the testplaque molded at 370 F. is 7 and, the test plaque molded at 450 F. has acolor indexnumber of 10.

Example 8 To a conventional prebodying pot or still is charged 71 partsof styrene monomer and 29 parts of acrylonitrile. The polymerization iscarried out in the presence of 0.1 part of a suitable chain transferagent at a temperature of 125 C. in an inert atmosphere for a period of4 to 6 hours until a conversion of 70% is achieved, the polymerizationis interrupted and the unreacted monomer is removed and the polymercooled. Employing the molding conditions of Example 1 on the resultantproduct, the color index number of the test plaque molded at 370 F. is 5and the test plaque molded at 450 F. has a color index number of 11.

Example 9 Example 8 is repeated with the addition before polymerizationof 0.05 part of 2,6 di-Z-isooctyl p-cresol and 0.1 part of substantiallyepoxidized dicyclopentadiene. Em ploying the molding conditions ofExample 1 on the resultant product, the color index number of the plaquemolded at 370 F. is 1 to 2 and the plaque molded at 450 F.'has a colorindex number of 3 to 4.

When styrene alone or other vinyl aryl compounds or mixtures thereof inamounts of 65 to 80% by weight to 35 to by weight of acrylonitrile areemployed in the above examples, similar advantageousresults areobtained.

From the foregoing, it will be obvious that the use of theaforementioned additives, i.e., an epoxidized composition and asubstituted phenol in the preparation of vinyl aryl and acrylonitrilecopolymers by any method results in molding compositions not readilysusceptible to discoloration under conventional molding conditions.

Many changes and alterations may be made without departing from thespirit and scope of this invention which is set forth in the appendedclaims which are to be construed as broadly as possible in view of theprior art.

We claim:

l. A thermoplastic polymeric composition readily moldable to clear andsubstantially non-discolored uniform products, consisting essentially ofthe polymerization product resulting from the polymerizationof fromabout to 80% of at least one polymerizable compound of the formula v R0x a wherein R is selected from the group consisting of hydrogen and themethyl radical, R is selected from the group consisting of chlorine andlower alkyl radicals and n is 0 to 2, and about 35% to about 20% byweight of acrylonitrile in the presence of and in contact with, based onthe combined weight of said polymerizable compound and acrylonit-rile,about 0.005% to 0.9% of at least one 2,4,6- tri-substituted phenol ofthe formula I ls wherein R R and R are selected from the groupconsisting of saturated aliphatic and aromatic hydrocarbon radicalscontaining no more than 12 carbon atoms and about 0.005% to 0.75% of anepoxidized organic composition selected from the group consisting of (a)resinous complex reaction mixtures of from 1 to 4 moles of an epihalohydrin per mole of a member selected from the group consisting ofpolyhydric phenols and polyhydric aliphatic alcohols, (b) epoxidizedoils resulting from the epoxidation of a member selected from the groupconsisting of (1) a glyceride reaction product of a fatty acid andglycerol and (2) a terpene oil and (c) low'molecular weight compositionsobtained by epoxidation of a cycloaliphatic compound other than aterpene oil, said cycloaliphatic compounds being free of vie-epoxyreactive substituents which interfere with the desired stabilization.

2. The thermoplastic polymeric composition of claim 1 wherein thepolymerizable compound employed in the polymerization is styrene.

3. The thermoplastic polymeric composition of claim 1 resulting from thepolymerizationof from about 30% to about of styrene, about 5% to about35% of alphamethylstyrene and about 35% to about 20% of acrylo:

nitrile. 4

4. The thermoplastic polymeric composition of claim '1 wherein theepoxidized organic composition used in combination with thetri-substituted phenol is a resinous complex reaction mixture of (a).

5. The thermoplastic polymeric composition of claim 1 wherein theepoxidized organic composition used in combination with thetri-substitut ed phenol is an epoxidized oil of (b).

6. The thermoplastic polymeric composition of claim 1 wherein theepoxidized organic compound is alow molecular weight composition of (c);

7. The thermoplastic polymeric composition of claim 1 wherein thepolymerization is conducted in aqueous suspension and the polymerizationis continued until conversion of monomers is between 60% and 92%.

8. The thermoplastic polymeric composition of claim 1 wherein thepolymerization is conducted in aqueous suspension employing from about0.2% to 2.0%, by weight of the combined monomers, of a water insolublealiphatic peroxide catalyst having the general formula wherein n is aninteger greater than 2 and the polymerization is continued untilconversion of monomers is between 60% and 92%.

9. The thermoplastic polymeric composition of claim 1 .resulting fromthe polymerization of from about 65% to about 80% of the polymerizablecompound of which about 5% to about 35% based on the total weight of theI composition may be alpha-methylstyrene, and about 35 to about 20% ofacr'ylonitrile.

References Cited by the Examiner UNITED STATES PATENTS 2,779,771 '1/57Phillips et a1. 260-458 2,804,444 8/57 Segto et a1. .4; 26045.7

10 LEON I. BERCOVITZ, Primary Examiner.

A. D. SULLIVAN, MILTON STERMAN, Examiners.

1. A THERMOPLASTIC POLYMERIC COMPOSITION READILY MOLDABLE TO CLEAR AND SUBSTANTIALLY NON-DISCOLORED UNIFORM PRODUCTS, CONSISTING ESSENTIALLY OF THE POLYMERIZATION PRODUCT RESULTING FROM THE POLYMERIZATION OF FROM ABOUT 65 TO 80% OF AT LEAST ONE POLYMERIZABLE COMPOUND OF THE FORMULA 